The following are the primary objectives of this research proposal: 1) To analyse at the light-microscopic and ultrastructural levels the interrelationships among tissues of the emerging cranio-facial region, using the mammalian (mouse) and avian (chick) embryos as model systems. 2) To examine experimentally using in vitro culture and grafting techniques the tissue-interactions which influence and direct morphogenesis and histogenesis in the cranio-facial region. 3) To experimentally alter normal tissue-interactons among tissues of the emerging cranio-facal region in order to analyse the effects of such interventions as a means of further elucidating the controlling factors in morphogenesis and histogenesis.